Primary hyperaldosteronism

Primary hyperaldosteronism was previously thought to be most commonly caused by an adrenal adenoma, termed Conn's syndrome. However, recent studies have shown that bilateral idiopathic adrenal hyperplasia is the most common cause. Differentiating between the two is important as this determines treatment.

Causes

• bilateral idiopathic adrenal hyperplasia: the cause of around 60-70% of cases
• adrenal adenoma: 20-30% of cases
• unilateral hyperplasia
• familial hyperaldosteronism
• adrenal carcinoma

Pathophysiology

• aldosterone is high
• renin is low (suppressed by volume expansion)
• consequences:
  • aldosterone → ↑ renal tubular sodium resorption (via ENaC channels in the collecting duct)
  • ↑ K⁺ excretion → hypokalaemia
  • ↑ H⁺ excretion → metabolic alkalosis
  • hypertension from sodium/water retention

Features

• hypertension
  • increasingly recognised but still underdiagnosed cause of hypertension
• hypokalaemia
  • e.g. muscle weakness
  • this is a classical feature in exams but studies suggest this is seen in only 10-40% of patients, and is more common with adrenal adenomas
• metabolic alkalosis

Investigations